The present invention relates to a directional drilling tool utilizing a drill string in a borehole and more particularly to such a tool wherein borehole deviation with respect to the vertical can be controlled to increase, decrease, or maintain the angle of such deviation without removal of the drill string from the borehole.
The technology developed with respect to drilling boreholes in the earth has long encompassed the use of various techniques and tools to control the deviation of boreholes during the drilling operation. In some instances such technology is employed to retard borehole deviation. In other instances increased directional deviation is desired. However, in virtually all instances it has heretofore been necessary to withdraw the drill string assembly from the borehole for the attachment of various specialized tools to achieve the desired objective. The prior art represented by such patents as the Page, Sr., et al. U.S. Pat. No. 2,891,769; the Farris et al. U.S. Pat. No. 3,092,188; the Fields U.S. Pat. No. 3,593,810; the Storm U.S. Pat. No. 2,686,660 and the Jeter et al. U.S. Pat. No. 3,424,256 evidence such operational limitations.
Drilling operations, particularly in petroleum exploration, are commonly carried out at great depths frequently reaching several thousand feet below the earth's surface. Since a drill string is composed of a multiplicity of sections of drill pipe which must successively be disassembled upon removal from the borehole, the removal of the drill string from the borehole for the attachment of directional tools at the remote end of the drill string in an extremely time consuming and thus expensive operation. Such procedures often entail several days of work. This "down time" is extremely expensive and a significant factor in the determination of the economic feasibility of exploratory drilling. The problem becomes chronic where, as is frequently the case, it is necessary to change the angle of borehole deviation several times requiring such considerable "down time" in each instance.
Therefore, it has a long been recognized that it would be desirable to have a directional drilling tool adapted for incorporation in a drill string individually or in any desired combination and capable of remaining inactive so as not to impede normal drilling operations, but subject to being activated to the extent desired without removal of the drill string from the borehole and which subsequently can similarly be deactivated without removal of the drill string from the borehole.